The hard outer covering (exoskeleton) of arthropods like insects, spiders, prawns and crabs is made of chitin. Chitin is a tough, light polymer built from a sugar called N-acetylglucosamine. It protects the body, supports it, and stops water loss. Memory hook: "Chitin = the CHITTY armour of insects; its brick is N-acetylglucosamine."
The arthropod body is covered by a hard exoskeleton made of chitin. Chitin is a polymer, and its single repeating unit is the sugar N-acetylglucosamine.
Your doubts, answered
What exactly is the arthropod exoskeleton made of?
It is made of chitin. Chitin is a long-chain polymer (many small units joined together). The small repeating unit is a nitrogen-containing sugar called N-acetylglucosamine. So the correct NEET answer to 'exoskeleton is made of' is chitin, not glucosamine (glucosamine is only the single building block, not the finished material).
Is chitin the same as cutin or cellulose?
No. This is the most common NEET mix-up. Cutin and cellulose are plant materials (cutin waterproofs leaves, cellulose builds plant cell walls). Chitin is an animal material found in the arthropod cuticle. If a question says 'exoskeleton of arthropods', the answer is always chitin, never cutin or cellulose.
What is the difference between chitin and N-acetylglucosamine?
N-acetylglucosamine is the single small brick. Chitin is the whole wall made by joining thousands of these bricks in a chain. NEET tests this: an option saying 'exoskeleton composed of N-acetylglucosamine' is treated as correct because chitin IS a polymer of N-acetylglucosamine, but if the choice is between 'chitin' and plain 'glucosamine', pick chitin.
Why do arthropods need an exoskeleton?
It gives protection (like armour), support for the body and muscles, and prevents water loss so they can live on land. But because it is hard and cannot grow, arthropods must shed it and make a new one to get bigger. This shedding is called moulting (ecdysis).
Is chitin living or non-living, and can it grow?
Chitin is a non-living secretion. Because it is dead and rigid, it cannot stretch or grow with the animal. That is why arthropods moult. This 'hard, non-growing armour' idea is exactly why moulting exists, and NEET links the two.
⚠️ The NEET trap ✗ Exoskeleton of arthropods is made of cutin or cellulose. ✓ It is made of chitin, a polymer of N-acetylglucosamine. 🧠 Cutin and Cellulose are the C-words for PLANTS. Chitin is the C-word for arthropod armour. If the animal is an insect or crab, the answer is chitin.
Real NEET questions
NEET 2022
Exoskeleton of arthropods is composed of:
A · Cutin
B · Cellulose
C · Chitin ✓
D · Glucosamine
Solution: In phylum Arthropoda the body is covered by a chitinous exoskeleton, so the answer is chitin. Cutin and cellulose are plant materials, while glucosamine is only the single monomer unit, not the finished exoskeletal polymer. Hence chitin is correct.
NEET 2016 Phase 1
Which of the following features is not present in Periplaneta americana (the cockroach)?
A · Schizocoelom as body cavity
B · Indeterminate and radial cleavage during embryonic development ✓
C · Exoskeleton composed of N-acetylglucosamine
D · Metamerically segmented body
Solution: The cockroach is an arthropod. It has a schizocoelom, a segmented body and a chitinous exoskeleton (chitin is a polymer of N-acetylglucosamine), so those options are true of it. Indeterminate and radial cleavage is NOT seen; arthropods show determinate, spiral cleavage. So option B is the feature that is absent.
NEET 2016 Phase 1
Which of the following features is not present in the Phylum Arthropoda?
A · Chitinous exoskeleton
B · Metameric segmentation
C · Parapodia ✓
D · Jointed appendages
Solution: Arthropods have a chitinous exoskeleton, a segmented body and jointed appendages. Parapodia are lateral swimming appendages of aquatic annelids like Nereis, not of arthropods. So parapodia is the feature not present in Arthropoda.
Solved Animal Kingdom NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Chitin, a tough non-living polymer of the sugar N-acetylglucosamine. It forms the hard cuticle covering insects, spiders, crabs and prawns.
Is chitin a protein?
No. Chitin is a polysaccharide (a chain of sugar units), not a protein. Its repeating unit is N-acetylglucosamine, a nitrogen-containing sugar.
Why can't arthropods grow inside their exoskeleton?
Chitin is hard and non-living, so it cannot stretch. To grow, the arthropod sheds the old exoskeleton and makes a bigger new one. This shedding is called moulting or ecdysis.
Chitin or glucosamine — which is the NEET answer?
If both appear as options, choose chitin. Glucosamine is only the building block; chitin is the actual exoskeletal material. But 'polymer of N-acetylglucosamine' also correctly describes chitin.
Do only arthropods have chitin?
Chitin is best known in the arthropod exoskeleton, but it also forms fungal cell walls. For NEET Animal Kingdom, link chitinous exoskeleton directly to Phylum Arthropoda.
